The metabolism of applied gibberellic acid in Pharbitis nil choisy: tentative identification of its sole metabolite as gibberellic acid glucoside and some of its properties

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Abstract
Radioactive gibberellic acid ([14C]GA3) applied to seedlings of Pharbitis nil strain Violet is converted to one single metabolite (R-[14C]GA3), which has been tentatively identified as GA3-glucoside. As with authentic GA3-glucoside, R-[14C]GA3 can be hydrolysed to some extent with cellulase and β-glucuronidase, but hardly at all with β-glucosidase. Acid hydrolysis, which is more effective than enzymatic hydrolysis, yielded GA3 as well as a biological inactive compound. The latter represents a degradation product of GA3 due to the sensitivity of GA3 to acidic conditions. The R-[14C]GA3, like authentic GA3-glucoside, possesses little or no biological activity. R-[14C]GA3 applied to developing seeds is partly hydrolysed during imbibition of the mature seed but is, however, reconverted to R-[14C]GA3 during subsequent germination. Applied R-[14C]GA3 is strongly accumulated in the cotyledons of Pharbitis seedlings, to a greater extent than [14C]GA3. However, unlike [14C]GA3 it is not accumulated in the apical regions of the hypocotyl. Furthermore no competition was observed between R-[14C]GA3 and [14C]GA3, which suggests that they do not compete for the same sites.